Field of the Invention
The field of the present invention is lenses providing extended depth of focus, particularly ophthalmic lenses such as contact lenses, corneal inlays or onlays, and/or intraocular lenses (IOLs).
Description of the Background
Presbyopia is a condition that affects the accommodation properties of the eye. As objects move closer to a young, properly functioning eye, the effects of ciliary muscle contraction and zonular relaxation allow the lens of the eye to change shape, and thus increase its optical power and ability to focus at near distances. This accommodation can allow the eye to focus and refocus between near and far objects.
Presbyopia, which normally develops as a person ages but which may additionally develop due to certain conditions of the eye, is associated with a sudden or progressive loss of accommodation. The presbyopic eye often loses the ability to rapidly and easily refocus on objects at varying distances. The effects of presbyopia usually become noticeable after the age of 45 years. By the age of 65 years, the crystalline lens has often lost almost all elastic properties and has only a limited ability to change shape.
Along with reductions in accommodation of the eye, age may also induce clouding of the lens due to the formation of a cataract. A cataract may form in the hard central nucleus of the lens, in the softer peripheral cortical portion of the lens, or at the back of the lens. Cataracts can be treated by the replacement of the cloudy natural lens with an artificial lens. An artificial lens replaces the natural lens in the eye, with the artificial lens often being referred to as an intraocular lens or “IOL”.
Monofocal IOLs are intended to provide vision correction at one distance only, usually the far focus. Predicting the most appropriate IOL power for implantation has limited accuracy, and an inappropriate IOL power can leave patients with residual refraction errors following surgery. Accordingly, it may be necessary for a patient who has received an IOL implant to also wear spectacles to achieve good far vision. At the very least, since a monofocal IOL provides vision treatment at only one distance and since the typical correction provided by the monofocal IOL is for far distance, spectacles are usually needed for good near and sometimes intermediate vision following implantation of a typical monofocal IOL.
The term “near vision” generally corresponds to vision provided when objects are at a distance from the subject eye of between about 1 to 2 feet are substantially in focus on the retina of the eye. The term “distant vision” generally corresponds to vision provided when objects at a distance of at least about 6 feet or greater are substantially in focus on the retina of the eye. The term “intermediate vision” generally corresponds to vision provided when objects at a distance of about 2 feet to about 6 feet from the subject eye are substantially in focus on the retina of the eye.
There have been various attempts to address the foregoing and other limitations associated with monofocal IOLs. For example, multifocal IOLs have been proposed that deliver, in principle, two foci, one near and one far, optionally with some degree of intermediate focus. Such multifocal, or bifocal, IOLs are intended to provide good vision at two distances, and include both refractive and diffractive multifocal IOLs. In some instances, a multifocal IOL intended to correct vision at two distances may provide a near add power of about 3.0 or 4.0 diopters, by way of non-limiting example.
Like monofocal lenses, multifocal lenses may take the form of an intraocular lens placed within the capsular bag of the eye, replacing the original lens or placed in front of the natural crystalline lens. Corrective monofocal or multifocal ophthalmic lenses may also be in the form of a contact lens or in the form of any other type of corrective lens placed not within the capsular bag of the eye, but rather placed external to but within the visual field of the eye.
Although multifocal ophthalmic lenses often lead to improved quality of vision for many patients, additional improvements would be beneficial. For example, some pseudophakic patients experience undesirable visual effects (dysphotopsia), e.g. glare or halos. Halos may arise when light from the unused focal image creates an out-of-focus image that is superimposed on the used focal image. For example, if light from a distant point source is imaged onto the retina by the distant focus of a bifocal IOL, the near focus of the IOL will simultaneously superimpose a defocused image on top of the image formed by the distant focus. This defocused image may manifest itself in the form of a ring of light surrounding the in-focus image, and is referred to as a halo. Another area in need of improvement revolves around the typical bifocality of multifocal lenses. More particularly, since multifocal ophthalmic lenses typically provide for near and far vision, intermediate vision may be compromised.
A lens with an extended depth of focus (EDOF, also referred to herein as extended depth of field) may remedy these disadvantages of known corrective lenses, at least in that an EDOF lens may provide certain patients the benefits of good vision at a range of distances, while having reduced or no dysphotopsia. Various techniques for extending the depth of focus of an IOL have been previously proposed. For example, some approaches are based on a bulls-eye refractive principle, and involve a central zone with a slightly increased power. Other techniques include an asphere or include refractive zones with different refractive zonal powers.
Although certain such lenses or lens combinations and/or treatments may provide some benefit to some patients, further advances, particularly with respect to EDOF lenses are desirable to benefit even more patients. For example, a further improved IOL lens which confers enhanced image quality across a wide and extended range of foci without dysphotopsia is desirable.